Polymer alloys phase-separating

Polymer alloys are generally named polymer blends within the polymer community. In a recent overview of such blends, Robeson (1994) points out that the primary reason for the surge of academic and industrial interest in polymer blends is directly related to their potential for meeting end-use requirements . He points out that, in general, miscible polymer pairs confer better properties, mechanical ones in particular, than do phase-separated pairs. For instance, the first commercial... 

Thus most of the time one obtains phase-separated systems in which the macromolecules of component A are not at all or only to a limited extent miscible with the macromolecules of component B, i.e., polymer A is incompatible or only partially compatible with polymer B. The synonymical terms polymer blend , polymer alloy , or polymer mixture denote miscible (homogeneous) as well as immiscible (heterogeneous) systems consisting of two or more different polymers. 

The majority of todays membranes used in microfiitration, dialysis or ultrafiltration and reverse osmosis cire prepared from a homogeneous polymer solution by a technique referred to as phase inversion. Phase inversion can be achieved by solvent evaporation, non-solvent precipitation and thermcd gelation. Phase separation processes can not only be applied to a large number of polymers but also to glasses and metal alloys and the proper selection of the various process parameters leads to different membranes with defined structures and mass transport properties. In this paper the fundamentals of membrane preparation by phase inversion processes and the effect of different preparation parameters on membrane structures and transport properties are discussed, and problems utilizing phase inversion techniques for a large scale production of membranes are specified. 

In this paper the discussion was concentrated mainly on the phase separation in polymer solutions due to the change of the composition of the mixture. The basic relations are also valid for phase separations induced by temperature changes, that is thermal gelation and can be applied to glass and metal alloys as well as to polymers. 

Small-angle X-ray scattering (SAXS) experiments using synchrotron radiation (SR) are performed at present mainly in the areas of real time scattering and anomalous dispersion.1 Typical applications are the study of melting or recrystallisation of semicrystalline polymers [4, 5], phase separation of alloys [6], muscle diffraction and stopped flow experiments on dissolved biopolymers [7, 8]. Anomalous dispersion has been exploited in order to determine partial structure factors in alloys [9] or polymers containing heavy atoms [10],... 

A miscible polymer blend is one for which the miscibihty and homogeneity extend down to the molecular level, so that there is no phase separation. An immiscible blend is one for which phase separation occurs, as described in the next section. An immiscible blend is called compatible if it is a useful blend wherein the inhomogeneity caused by the different phases is on a small enough scale not to be apparent in use. (Blends that are miscible in certain useful ranges of composition and temperature, but immiscible in others, are also sometimes called compatible blends.) Most blends are immiscible and can be made compatible only by a variety of compatibilisation techniques, which are described in section 12.2.4. Such compatibilised blends are sometimes called polymer alloys. 

Phase separation in binary alloys, polymer blends, and fluid mixtures has been studied intensively for many years [148]. It takes place when a two-component mixture is quenched from a disordered state into a two-phase coexistence region. After such a quench, composition fluctuations are created that grow and form domain structures. In the late stages, the domain structure coarsens in time, a process that is driven by the interfacial tension coexisting phases. The growth of the characteristic length scale R t) follows a power-law behavior,... 

Polymer alloys often exhibit microphase separation. The heterogeneous morphologies are determined not only by the composition of the system but by the processing conditions as well. The microstructure influences the properties of polymeric alloys [40]. For example, the addition of a second phase of dispersed rubbery particles into the polymer matrix results in a great enhancement of toughness [41]. 

Several interesting observations relate to such thermodynamic measurements. For example, the exothermic effects, associated with phase separation in LCST-type polymer blends, showed a correlation between the exothermic enthalpy and the interactions between the components (Natansohn 1985) however, the specific interaction parameter xn was not calculated. In another example, there are definitive correlations between the thermodynamic and the transport properties (see Chap. 7, Rheology of Polymer Alloys and Blends ). Thermodynamic properties of multiphase polymeric systems affect the flow, and vice versa. As discussed in Chap. 7, Rheology of Polymer Alloys and Blends , the effects of stress can engender significant shift of the spinodal temperature, AT = 16 °C. While at low stresses the effects can vary, i.e., the miscibility can either increase or decrease. 

In a typical formulation, an ethylene-n-butylacrylate-carbon monoxide (60/30/ 10) terpolymer (60 wt%) is melt compounded in a twin-screw extmder with PVC (30 wt%) along with an optional, nonvolatile plasticizer such as trioctyl trimellitate (10 wt%) such that the ethylene terpolymer dispersion was cured in situ during the mixing by catalytic amounts of a suitable peroxide (0.3 %) and a bismaleimide crosslink promoter (0.2 %). It is believed that the initial homogeneous miscible melt blend later forms the micro phase-separated mbber domains as the selective rubber cross-Unking progresses. Currently, such TPV blends are commercially sold as Alcryn melt-processable rubbers by Advanced Polymer Alloys division of Ferro. 

Polymer alloys and composites have become an attractive research field world-wide because of their practical and theoretical significance. Miscibility and phase separation arc the key topics in this field. With the development of criterion techniques for miscibility, complicated phase diagrams for polymer blends were obtained which cannot be explained by the... 

This is a three-part book with the first part devoted to polymer blends, the second to copolymers and glass transition tanperatme and to reversible polymerization. Separate chapters are devoted to blends Chapter 1, Introduction to Polymer Blends Chapter 2, Equations of State Theories for polymers Chapter 3, Binary Interaction Model Chapter 4, Keesome Forces and Group Solubility Parameter Approach Chapter 5, Phase Behavior Chapter 6, Partially Miscible Blends. The second group of chapters discusses copolymers Chapter 7, Polymer Nanocomposites Chapter 8, Polymer Alloys Chapter 9, Binary Diffusion in Polymer Blends Chapter 10, Copolymer Composition Chapter 11, Sequence Distribution of Copolymers Chapter 12, Reversible Polymerization. 

Liu Y-M, Xu J-T, Fu Z-S, Fan Z-Q (2012b) Effect of phase separation on overall isothermal crystallization kinetics of PP/EPR in-reactor alloys. J Appl Polym Sci 127 1346-1358... 

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